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The area of the cylinder piston, in square inches, will be found by the following formula:

α=

4.24 n A/PS
ps (1-f)

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In which s denotes the

(12.)

stroke of the piston in feet, and f=friction, working pumps, and per cent., which, in this intended steam engine, will be f=0.32 per cent. Let the proportions of stroke and diameter of the piston be as 2 to 3, we have the diameter in inches:

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Say 56 inches diameter and 36 inches stroke, the effect of the steam engine, in horse power:

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Cut off the steam at one-third of the stroke, c being the cubic feet of steam for each revolution, and k denotes the volume of steam compared with water at the given pressure.

C=

562 x 0.785 × 12×4

1728

The consumption of coal, if anthracite, will be:

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That is when one pound of anthracite coal evaporates 8 pounds of water per hour; or call the number of pounds of water =w, evaporated per pound of coal, we have for x,

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Plate XIII. represents a section of a vessel, of the aforesaid dimensions. On the bottom lays two inclined, direct action, condensing steam engines.

A, The Engineer's Room.

B, First Class Cabin.

C, Ventilator and Sky-Light.
D, State Rooms.

E, Store Rooms.

F, Passages.

G, House on Deck.

H, Berths.

The engine is manoeuvered in the engine room A, by the three rods a, b, and c, which run through the columns in the engineer's room.

The four gauges on each side are the steam gauge, vacuum gauge, water gauge for the boiler, and salinometer; in the front is a clock and

counter.

a is for regulating the injection water, connected with the injection cock k.

b for reversing the eccentrics, to back and go ahead, connected with a conical cog wheel.

c for regulating the steam to the engine; by the same rod steam can be given to full stroke.

d Cylinder heads.

e Injection water pipe.

f Steam pipe.
g Steam chest.
h Exhaust pipe.
i Discharge pipe.
k Injection cock.
l Condenser.

m Air pumps, double and direct action.

n Feed and Force Pumps, double and direct action.

o Air vessels.

p Eccentrics for the steam valves.

q Frames and guides.

Steam cylinders.

The engines are working on a double crank, represented in fig. 9. The scale is 3-inch to a foot. The cranks are opposite to each other; therefore the steam engines do not work at right angles; but if it is thought more desirable that they should, the cranks can be set in any angle; this is a matter of small consequence compared with the friction in the bearings a and d, which the opposite cranks prevent, and it is the reason why the stroke of the piston can be taken so short in proportion to the diameter.

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Now for the strength of this crank, which, at first sight, promises little for durability. Let the end a be the continuation of the propeller shaft, and the steam engines be applied at b and c; let the force which is applied at c be denoted by the letter c. The force which acts to twist the crank

at b will be cs; but as there is a bearing at d, the resistance at b acts to twist the crank at c with a force = bs; if the crank should break, the force c must break it both at c and b at the same time, which will require

CS

twice the power that would break it only at b; or will be the force by

2

which the crank should be twisted at b, which is exactly the same as the force c applied to b, to twist the shaft at a, or if the diameter at a, b, and c be equal, the strength of the opposite cranks will be the same as a common single crank.

Let D be the diameter of the propeller shaft in inches, and of wrought iron.

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The diameter at d will be the same as the diameter for a crank pin of a common single crank; or

d=✓D2+1·282—1·18.

d=√122+1·2 × 32 — 1·1 × 3=8.5 inches.

(17.)

This kind of crank was tried and tested by a Swedish Engineer, O. E. Carlsund, and the results were most satisfactory. The engines were 30 inches in diameter and 18 inches stroke; they made from 105 to 110 revolutions per minute. The air pumps were direct action, working at the same speed with 18 inches stroke; pressure in the boiler, 30 pounds to the square inch, cutting off at one-third of the stroke; the air pumps and valves worked silently.

In direct action propeller engines, the arrangement of the air pumps. and their valves, is of the greatest importance. Many engineers are of the opinion that the more vacuum the better. There is, however, an

exception with propeller engines, when the engines and air pumps are direct action. As an example, in an experiment made by the same engineer, O. E. Carlsund, he placed a small cock on the condenser; while the steam engine was working with a good vacuum he opened the cock, letting in a little air to the condenser. The number of revolutions increased from 15 to 20 per cent.; the cause of it, I leave to engineers for solution.

When an air pump makes more than n double strokes per minute, it does not work well, or rather works to a disadvantage. This number n, will be found by the formula

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in which a denotes the area of the valves, and A= area of air pump piston; being the stroke of air pump piston in feet. P= pressure in the condenser.

When the number of double strokes per minute are given, the area of the valve will be

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When we get from this formula a=A or a>A the air pump will work with disadvantage; or when the valve a is applied in the air pump piston, we only get a= A then, 5 and p are the only quantities which can be modified, and s will be

121 a

n A p.

(20.).

In the steam engine represented on plate XII. the valves are round and move on vertical spindles. The stroke of the air pump piston is equal to the stroke of the cylinder piston, and the diameter is 14 inches. In that case, the diameter of the valve must be calculated, and will be as follows:

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or, say 11 inches, as the spindle in the centre takes a few square inches. These formulæ, (18, 19, 20, 21,) undergo a little modification with different arrangements of condensers and air pumps, for instance, if the air pumps are vertical or horizontal.

In this steam engine, the air pumps have an inclination of 16 degrees to the horizon.

It is of no consequence what angle the steam engines make with each other but rather make it to suit the bottom of the vessel. There will always be angle enough for one engine to help the other over the centre, and the greater the angle the better for the friction in the bearings. With those kind of steam engines, there is sufficient room in the breadth of any vessel to get the connecting rod twice the stroke. The entire engine comes below the load line, and makes an arrangement with every con

venience.

Under full motion, all the parts of the machinery are accessible for the engineer. The weight of the engines, including air pumps and condensers, will be, stationary parts, 22 tons, moving or working parts, 8 tons, total weight, 30 tons; occupying a space in the length of the vessel of only 8 feet 4 inches. Lower hold is 12 feet; on the first deck, 7 feet; on the second deck, 8 feet.

28*

A Table of Equations Collected for Convenience and Reference.

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